1. Field of the Invention
The invention relates to gypsum plaster compositions with improved adhesion to plastic surfaces and metal surfaces, and to their use.
2. Description of the Related Art
It is known that the adhesion of cement mortars to various substrates is increased by adding film-forming polymers This effect is successfully utilized in modified thin-layer mortars, for example, and in exterior insulation systems. In addition to the aqueous dispersions used for this purpose there are also spray-dried dispersions known as dispersion powders. After addition of dispersion powder, cement-based mortars also adhere to PVC substrates and wood substrates (J. Schulze, TONINDUSTRIE-ZEITUNG 9, 1985). Gypsum trowelling compounds are often used as joint fillers for filling the joints between plasterboard. Although the addition of dispersion powders to gypsum trowelling compounds increases the adhesion to masonry, gypsum substrates, and concrete, the simple addition of dispersion powders does not increase adhesion to other substrates such as plastics, for example rigid PVC, or to metal substrates like aluminum sheet, or increases adhesion to such substrates only marginally. Even when using a high proportion of dispersion powder, no adhesion is achieved on sheet aluminum, and adhesion to other substrates, for example PVC, is also low.
It would be desirable to provide gypsum trowelling compounds which adhere to both plastic and metal substrates.
It has now been surprisingly discovered that the addition of salts of lower fatty acids in combination with dispersion powders, markedly increased the adhesion of gypsum trowelling compounds to these substrates. Calcium formats has been used as an accelerator for cement setting in cement mortars. However, this effect as an accelerator is not known to be applicable to gypsum-based compositions.